If a "fake bidder" wins an auction, they are legally obliged to follow through with the purchase. Shill bidders on the other hand can be prosecuted by law as it is a highly illegal practice.
Question for Oscar: Have you considered legally forcing the fake bidders to follow through with their purchase?
Ebay would never force or allow a buyer to be forced to pay, short of taking someone to court, it wont happen.
There is no legal obligation for a buyer to go through with the sale, you can't force someone to pay for anything they don't want.
Realistically it is just easier to move on a re-list, hoping the buyer doesn't decide to leave you bad feedback just for the hell of it.
I sold an item ( a lousy $15 dollars worth) that got stolen before I could send it, I immediately refunded the buyers money, profusely apologised and left them excellent positive feedback, yet they still saw fit to leave me neutral feedback 3 weeks after the auction end, and Ebay wouldn't do a thing about it.
Ebay is for buyers, sellers are just a necessary evil ripe for the fleecing as far as Ebay is concerned.
